Actuator with torque limiter

ABSTRACT

An actuator includes: at least one drive motor; an outlet ( 22 ); an adjustable torque limiter which is disposed between the/each motor and the outlet ( 22 ), the torque limiter having a mobile element ( 100 ) which is used to set the maximum torque transmitted; and a case which houses the motor and the torque limiter. The case is provided with an opening ( 110 ) for accessing the mobile element ( 100 ) used to set the maximum torque transmitted and the torque limiter is mounted in the case.

FIELD OF THE INVENTION

The present invention relates to an actuator of the type comprising:

-   -   at least one drive motor;    -   an output member;    -   an adjustable torque limiter which is interposed between the or        each motor and the output member, the torque limiter comprising        a movable member for adjusting a maximum transmitted torque; and    -   a housing which contains the or each motor and the torque        limiter.

BACKGROUND OF THE INVENTION

In a number of fields, it is necessary for actuators to be provided witha torque limiter. This torque limiter is constituted, for example, byfriction members which are held compressed together, the compressionforce of these friction members defining the sliding torque betweenthese two members. The torque transmitted is limited to the slidingtorque.

In practice, it is advantageous for the torque limiter to be calibratedbefore assembly. In an actuator, the torque limiter is generallypreceded and/or followed by other reduction gear members, such as anepicyclic reduction gear, or reduction steps which are provided betweenthe drive motor(s) and the torque limiter.

Owing to the machining differences between the various components whichcan be used from one actuator to another, it is difficult to determineby means of calculation the calibration of the torque limiter inaccordance with the other elements of the actuator in order to ensure amaximum predetermined torque at the output member of the actuator.

SUMMARY OF THE INVENTION

The object of the invention is to provide an actuator which allows thelimit torque measured at the output member to be fixed in a precisemanner, independently of the production quality of the various memberswhich are present in the kinematic chain between the drive motor(s) ofthe actuator and the output member.

To this end, the subject-matter of the invention is an actuator of theabove-mentioned type, characterised in that the housing has an openingfor access to the movable member for adjusting the maximum torquetransmitted whilst the torque limiter is mounted in the housing.

According to specific embodiments, the actuator further comprises one ormore of the following features:

-   -   the adjusting member comprises a nut and the torque limiter        comprises a shaft having a threaded portion, the nut is screwed        on the threaded portion, the axial position of the nut on the        threaded portion defining the maximum torque transmitted, and        the actuator comprises corresponding recesses which are provided        in the shaft and in the nut, as well as a member for fixing the        nut on the shaft, which member is engaged in the corresponding        recesses, in the direction of the shaft;    -   the fixing member comprises a support which is arranged at the        end of the shaft, which support carries at least one locking        finger which is engaged in two corresponding recesses;    -   it comprises a screw for retaining the fixing member, which        screw is engaged in a threaded hole which is provided in the        shaft;    -   it comprises a removable plug for closing the opening; and    -   it comprises at least one reduction step between the or each        motor and the output member.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be better understood from a reading of the followingdescription, given purely by way of example and with reference to thedrawings, in which:

FIG. 1 is a partially cut away perspective view of an actuator accordingto the invention;

FIG. 2 is a longitudinal sectioned view of the actuator of FIG. 1;

FIG. 3 is a partially cut away perspective view of the differentialreduction gear and torque limiting mechanism of the actuator of FIGS. 1and 2;

FIG. 4 is an exploded perspective view of the mechanism of FIG. 3; and

FIG. 5 is a longitudinal sectioned view of the mechanism illustrated inFIGS. 3 and 4.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The actuator 10 illustrated in the Figures is intended for locking anundercarriage of an aircraft in a retracted position.

This actuator comprises a housing 12, inside which two drive motors 14A,14B are arranged, each of which is connected mechanically to adifferential reduction gear and torque limiting mechanism 15. Thismechanism comprises a differential reduction gear 16 which includes atorque limiter 18. The actuator further comprises an epicyclic reductiongear 20 which is driven by the mechanism 15 and a rotating output member22 which protrudes from the housing 12 and which is itself driven by theepicyclic reduction gear 20.

More precisely, the two motors 14A, 14B are constituted by electricmotors whose stators 24A, 24B are fixedly joined to the housing 12 andwhose rotors 26A, 26B can be rotatably moved about axes Y1-Y1 and Y2-Y2which extend parallel with each other.

The output shafts 28A, 28B of the motors drive the first and secondmotor sun pinions 30A, 30B of the differential reduction gear 16. Thesemotor sun pinions can rotate around the same principal axis X-X whichextends parallel with the axes Y1-Y1 and Y2-Y2 of the motors.

As illustrated in FIG. 2, the output shaft 28A of the motor is coupledto the motor sun pinion 30A in order to be caused to rotate by means ofa reduction step 32A which is constituted by two coaxial and fixedlyjoined pinions 34A, 36A which have different diameters.

Similarly, as illustrated in FIG. 1, the output shaft 28B of the motoris coupled in terms of rotation to the motor sun pinion 30B by means ofa reduction step 32B which is constituted by two coaxial pinions 34B,36B which have different diameters and which are fixedly joined by ashaft 38.

The speed differential reduction and torque limiting mechanism 15 isillustrated alone in FIGS. 3 to 5. It has an output shaft 40 whichextends along axis X-X. This shaft has, at a first end, an output pinion42 which can drive the epicyclic reduction gear 20.

The two motor sun pinions 30A, 30B are mounted so as to rotate freelyabout the output shaft 40. The axes of the pinions 30A, 30B and theoutput shaft 40 are identical. The pinions 30A, 30B are supported bythis shaft and are guided in rotation about the shaft by slidingbearings or rolling bearings 44A, 46A and 44B, 46B having lateralshoulders for axial retention.

Clamping jaws 48A, 48B are arranged between these bearings and the shaft40. These jaws are constituted by sleeves 50A, 50B which are extended atthe facing ends thereof by integral collars 52A, 52B. The jaws 48A, 48Bare connected in terms of rotation to the shaft 40 but are free to slidein translation along the length thereof. To this end, complementaryprofiles, such as flat portions, are provided on the outer surface ofthe shaft 40 and on the inner surface of the jaws 48A, 48B.

The differential reduction gear 16 comprises, between the two motor sunpinions 30A, 30B, a planet carrier 60 which is constituted by twoend-plates 62A, 62B which are fixedly joined to each other in terms ofrotation by means of pins and screws 63. Between the two end-plates 62A,62B of the planet carrier, there are mounted pairs of planet pinions64A, 64B which engage with each other and each of which engages with asmall driving sun pinion 70A, 70B which is fixedly joined to the motorsun pinion 30A and 30B, respectively.

Each planet pinion is in fact formed by two identical coaxial andintegral gears which are carried by a shaft 72, with which they areintegral.

The shafts 72 can rotate about themselves relative to the end-plates62A, 62B, between which they are held by means of bearings 74. Theshafts 72 extend parallel with each other and parallel with the axis X-Xof the output shaft 40. The axes of the shafts 72 are different from theaxis X-X so that the planet pinions 64A, 64B can rotate together as anassembly about the axis X-X.

A hub 80 is fixedly joined in terms of rotation to the planet carrier 60by means of the pins 63. This hub is mounted so as to be able to rotateabout the shaft 40. It is arranged between the two motor sun pinions30A, 30B. The hub 80 can be seen more clearly in FIG. 4. It is of planarform with a generally annular core which is extended by twodiametrically opposed lateral lugs 80A, through which the pins 63extend. The pinions 64A, 64B are arranged around the core in theopenings provided between the lateral lugs 80A.

The hub 80 comprises two friction discs 82A, 82B which are attached bymeans of adhesive bonding at the opposing planar surfaces thereof. Theyare held compressed between the collars 52A, 52B of the jaws 48A, 48B,these collars forming friction members which can co-operate with thefriction discs over planar annular surfaces.

The output shaft 40 is supported by means of ball bearings 90A, 90Bwhich are arranged at one side and the other of the mechanism 15. Theseball bearings are supported by the housing 12. The shaft 40 has a collar92 which can be axially supported on the ball bearing 90B which isaxially supported on a shoulder of the housing 12.

The hub 80 is axially clamped between the two jaws 48A, 48B. The jaw 48Bis supported on the collar 92 by means of a stack of Belleville washers94B and a rigid washer 96B.

The jaw 48A is pressed by means of a rigid washer 96A and a stack ofBelleville washers 94A. This stack carried by the shaft 40 is keptclamped by means of a nut 100 which is screwed and centered on thesecond end of the shaft 40 opposite that which presses against thepinion 42. The ball bearing 90A is engaged around this nut 100 over alength of the nut which has a smooth surface at the outer side.

In this manner, the nut 100 brings about axial retention of the hub 80which is clamped between the two jaws 48A, 48B. The jaws are urgedtowards each other by the Belleville washers 94A, 94B, by means of thesupport washers 96A, 96B. The Belleville washers are held compressed atone side by the collar 92 and, at the other side, by the nut 100.

Depending on the tightening of the nut 100, the Belleville washers arecompressed to a greater or lesser extent and the pressure which theyapply to the jaws 48A, 48B can be adjusted in such a manner that thefriction force between the jaws 48A, 48B and the friction discs 82A, 82Bis modified.

In order to adjust the friction force, the housing 12 has an opening 110which is provided in the extension of the output shaft 40 and whichallows access to the nut 100 and allows it to be operated with aspanner. In order to bring about the fixing of the nut, the shaft 40has, at the second end thereof which carries the nut, transverserecesses 112 which open at the end of the shaft. There are, for example,three recesses. Corresponding recesses 112, 114 are provided in the nut100. They also open at the end of the nut.

A locking member 120 constituted by a collar 122 which carries twolocking fingers 124 is engaged at the end of the shaft in such a mannerthat the fingers are received in corresponding radial recesses which areprovided at the end of the shaft 40 and in the nut 100.

A screw 126 is engaged in a threaded hole 128 which is arranged axiallyat the end of the shaft. Screw 126 extends through the locking member120 and brings about the retention of screw 126.

The opening 110 is closed by means of a removable and leak-tightprotection plug 140.

The actuator operates in the following manner.

When the two motors rotate at the same speed, the two motor sun pinions30A, 30B are driven in the same direction. In this manner, theassociated planet pinions 64A, 64B of the same pair are stationaryrelative to each other. The planet carrier 60 is caused to rotate by theplanet pinions which are themselves caused to rotate about the shaft X-Xby means of the driving sun pinions 70A, 70B.

The hub 80 is then caused to rotate with the planet carrier 60.

The torque which is provided by the motors is transmitted from the hub80 to the shaft 40, as long as the friction force applied between theclamping jaws 48A, 48B and the friction discs 82A, 82B is greater thanthe torque supplied by the motors.

If this torque provided by the motor is greater than the friction forceapplied by friction, the friction discs slide over the friction surfacesof the jaws in such a manner that only a portion of the torque istransmitted. Therefore, the hub clamped between the clamping members48A, 48B forms a torque limiter which is interposed between the twomotor sun pinions 30A, 30B.

If one of the motors rotates at a different speed relative to the othermotor, or if one of the motors is stopped, the two driving sun pinions70A, 70B rotate at different speeds so that the planet pinions 64A, 64Bare caused to rotate about themselves in opposite directions, whichcompensates for the difference in the speed of rotation of the twomotors. The planet carrier 60 is then driven at a mean speed between thespeeds of the two motor sun pinions 30A, 30B, which thus drives theshaft 40 at this speed as long as the torque provided by the motors isless than the friction torque applied by the friction surfaces which arein contact.

As known per se, the shaft 40 drives the control member 22 via theepicyclic reduction gear 20.

Since the torque limiter is interposed between the two motor sun pinions30A, 30B, the space taken up by the reduction gear and torque limitingmechanism is reduced, which allows an actuator to be produced whichgenerally takes up a small amount of space.

In order to bring about the adjustment of the torque limiter, the plug140 is removed, thus allowing access to the screw 126. The screw 126 isremoved as well as the locking member 120. The nut 100 is screwed orunscrewed in order to bring about a suitable clamping force for the twojaws 48A, 48B on the friction discs 82A, 82B.

After the position of the nut has been adjusted, the locking member 120is engaged once more in corresponding recesses 112, 114 of the nut andthe end of the shaft, and the screw 126 is retightened in order to bringabout axial retention of the locking member 120. The plug 140 is finallyrepositioned in order to ensure the leak-tightness of the housing.

It will thus be appreciated that, in an actuator of this type, thetorque limiter can be calibrated after the actuator assembly has beenassembled, thereby allowing friction and losses of efficiency caused bythe various engaged elements which constitute the actuator, and inparticular the pinions of the epicyclic reduction gear 20, to be takeninto account. In this manner, the maximum output torque of the actuatormeasured in the region of the output member 22 can be defined in aprecise manner regardless of the machining quality of the various movingelements of the actuator.

1. Actuator comprising: at least one drive motor; an output member; anadjustable torque limiter which is interposed between the at least onemotor and the output member, the torque limiter comprising a movablemember for adjusting a maximum transmitted torque; a housing whichcontains the at least one motor and the torque limiter, the housinghaving an access opening for access to the movable member for adjustingthe maximum torque transmitted whilst the torque limiter is mounted inthe housing; and a removable plug for closing the access opening,wherein the movable member comprises a nut and the torque limitercomprises a shaft having first and second ends, a threaded portion beingat said second end, the nut being screwed on the threaded portion, saidsecond end and said movable member being arranged entirely inside thehousing such that an axial geometric projection of the second end of theshaft extends through the access opening.
 2. Actuator according to claim1, wherein the axial position of the nut on the threaded portion definesthe maximum torque transmitted, and wherein the actuator comprisescorresponding recesses which are provided in the shaft and on the nut,as well as a member for fixing the nut on the shaft, said member isengaged in the corresponding recesses, in the direction of the shaft. 3.Actuator according to claim 2, wherein the fixing member comprises asupport which is arranged at the end of the shaft, which support carriesat least one locking finger which is engaged in two correspondingrecesses.
 4. Actuator according to claim 3, further comprising a screwfor retaining the fixing member, said screw is engaged in a threadedhole which is provided in the shaft.
 5. Actuator according to claim 2,wherein the screw is screwed on one end of the shaft, and the recessesof the shaft are transverse recesses which open at the end of the shaft.6. Actuator according to claim 5, wherein the recesses of the nut openat the end of the nut.
 7. Actuator according to claim 1, furthercomprising at least one gear reduction between the at least one motorand the output member.
 8. An actuator comprising: two drive motors; anoutput member; an adjustable torque limiter which is interposed betweenthe two driver motors and the output member, said torque limitercomprising a shaft having a threaded portion at one end; a nut screwedinto said threaded portion, said nut adjusting the maximum transmittedtorque; a housing which contains at least the torque limiter, saidhousing having an opening adjacent said one end of the shaft for accessto the nut, said nut and said torque limiter being entirely within thehousing; and a removable plug for closing said opening.